1. The Field of the Invention
The present application relates to protective laminates and coating. More particularly, the present invention relates to durable optically transparent laminates for protecting windshields from damage due to gravel, rocks or other debris impacting the windshield.
2. The Relevant Technology
Every year, millions of windshields are damaged by rocks or other debris that impact the windshield. Winter is particularly hazardous in many areas where environmental constraints on the use of salt to control icy surfaces result in a great deal of sand or other solid substances being used. Sand, natural rubble and construction debris have created a year-round hazardous situation for glass (and/or laminated) windshields in any overland vehicle or glass in other equipment, as the sand and other solid debris are thrown up and collide with windshields.
If the damage is slight, such as a small chip in the windshield, it can often be repaired in situ. Greater damage, such as larger chips and cracks, may require the windshield to be replaced. The cost of repairing or replacing a windshield can range up to hundreds of dollars or more. Accordingly, there is a continuing need for improved coatings and methods that can reduce windshield replacements by protecting against windshield damage from impacting debris.
Previous attempts to provide exterior films to protect windshields from damage have failed or are limited for a number of reasons. Such reasons include, for example, that the films: do not cover the entire glass; do not adhere well to the glass; do not readily conform to a curved windshield; are not UV stable over the long term; are readily scratched by windshield wipers and/or car wash brushes; and/or have poor optical quality due to inferior film or adhesive restrictions.
For example, U.S. Pat. No. 6,634,695 (“the '695 patent”) discloses an impact resistant barrier around the periphery of a windshield. Barrier materials disclosed in the '695 patent include clear polymeric films as well as opaque materials such as rubber, plastic, or metal. Particularly, one suitable barrier material disclosed by the '695 patent is SCOTCHCAL™, an 8 mils thick polyurethane film sold by 3M. By limiting the extent of these clear and opaque barriers to the periphery, high visibility is maintained in the center of the windshield while protection is provided around the periphery. This approach is clearly limited in that such barriers are not suitable to cover the entire windshield. Thus, in order to maintain a suitable visibility where the barrier materials are applied, the '695 patent limits itself to protecting only those portions of the windshield where high visibility is not necessary.
Attempts thus far at providing a clear protective film to cover an entire automobile windshield have failed for various reasons, typically because the suggested films are not sufficiently transparent, distort the view, are not UV stable, or scratch easily. For example, the transparent laminate materials currently commercially available as Scotchgard Anti-Graffiti Window Film AG-4 and Scotchgard Anti-Graffiti Window Film AG-7 from 3M Corporation were tested for windshield applications. These films were found to be unsuitable because they do not provide sufficient scratch resistance for windshield applications and the underlying PET is not UV stable. Under the demanding conditions windshield use can place upon a laminate film, the AG-4 and AG-7 were both been found to degrade and scratch more than is acceptable.
Accordingly, there is a continuing need for new and improved methods and coatings to protect an entire windshield from damage without significantly reducing the optical qualities of the windshield.